Many portable electronic products today use battery power for operation. In many applications, especially products with real time clocks, certain circuits must operate even when the product is in an OFF mode. These circuits would need to have a low current drain to preserve battery life.
Differential amplifiers with selectable hysteresis are known which allow the hysteresis trip voltages to be determined by a ratio of transistor emitter areas. A circuit of this type, shown in FIG. 1, provides a controlled hysteresis with low current drain, but the circuit is functional only over a narrow range of input voltages. Unless the input voltages are within the narrow range centering around one-half of a diode voltage drop, the circuit cannot function.
Thus, what is needed is an amplifier with hysteresis and an extremely low current drain capable of operating over a sufficiently large input voltage dynamic range.